Sampling device for mass spectrometric analysis

ABSTRACT

A device for vaporizing a liquid for analysis, consisting of a tubular member having an inlet with a reduced bore and a tapered evaporation portion, and is connected with a vacuum source and mass spectrometer. The device facilitates the automated analysis of a large number of samples.

United States Patent Thurston [451 Aug. 1, 1972 1541 SAMPLING DEVICE on MASS [56] mam cm T T S ASIALYSIS I UNITED STATES PATENTS [72] Deep 2,922,306 1/1960 Crable 2so/41.9 [73] Assignee: Atomic Energy of Canada Limited, Primary Examiner-James W. Lawrence Ottawa, Ontario, Canada Assistant Examiner-C. E. Church 22 Filed: March 3, 1969 3' 9 [21 Appl. No.2 803,635 v TRA T I I A device for vaporizing a liquid for analysis, consisting 52 us. c1. ..2s0/41.9 s 73/425.6 122/4' tubular member having inlet with a reduced 7 250743 5 bore and a tapered evaporation portion, and is con- [511 Int. Cl j 39/34 B01 d 5/44 nected with a vacuum source and mass spectrometer. The device facilitates the automated analysis of a large [58] Field of Search ..250/4l.9 S, 73/4215, number of samples 4 Claims, 4 Drawing Figures SAMPLING DEVICE FOR MASS SPECTROMETRIC ANALYSIS This invention relates to a sample vaporizing device, and in particular to a sample vaporizing device to facilitate automated mass spectrometric analysis of water for the determination of the deuterium content thereof.

Prior to the present invention the mass spectrometric analysis of samples was performed by introducing a sample into a sealed container, vaporizing the entire sample by heating, introducing the vapor into a spectrometer and subsequently purging the container and spectrometer before the introduction of another sample.

A major difficulty in automating mass spectrometric analysis has been the problem of inserting a representative sample in the spectrometer. For analysis the sample must be in the vapor state. Because isotopic fractionation occurs at a liquid-vapor interface or water evaporator, it has been necessary, using normal procedures, to totally evaporate a sample of water before introduction into a spectrometer. The automation of such a procedure would require eleborate equipment.

In the production of heavy water it is advantageous to analyze a large number of water sources to determine the deuterium content. The present device facilitates an automated procedure for analyzing a large number of samples rapidly.

The invention consists of an elongated tubular member having an inlet portion with a reduced bore, a central evaporation portion and an outlet portion for connection with a vacuum source and an analyzing device, said central portion having a bore of increasing cross-sectional area from the inlet portion to the outlet portion.

For vaporizing water the inlet portion will have a bore diameter of less than 60.microns and preferably from 20 to 30 microns.

The invention also consists of an apparatus comprising a tubular member having an inlet portion with a reduced bore, a central evaporation portion having a bore increasing cross-sectional area from the inlet portion to an outlet portion, connected to first and second passage means, said first passage means connected to a sample analyzing device and said second passage means connected to a vacuum source, and valve means releasably blocking said second passage.

In addition the apparatus includes means to move sample containers successively into position relative to said tubular member, means to move said tubular member in and out of contact with the sample containers, and means to shutoff and open said valve means in accordance with the position of said tubular member.

The invention also consists of a method of vaporizing a liquid sample for analysis using a vaporizing device comprising a reduced inlet portion, a tapered vaporizing portion and an outlet portion connected with a vacuum source and an analyzing device, comprising the steps of drawing the sample into the vaporizing device with the vacuum source until equilibrium in the tapered evaporation portion has been established, shutting off the vacuum source to allow the vaporized sample to enter the analyzing device, performing the analysis, and applying the vacuum to purge the analyzing device.

Preferably the method comprises the further step of removing the inlet portion from the sample and moving, a second sample into the position, relative to the vaporizing device, occupied by the first mentioned sample.

The vacuum source preferably provides a pressure between 0.01 torr and 7 torr.

Preferably the meniscus in the evaporation portion is kept below 1 mm in diameter.

The above method in particular is for samples of water containing deuterium.

The invention will now be described by way of example, with reference to the accompanying drawings in which:

FIG. 1 is an enlarged side view of the sample vaporizing device.

FIGS. 2 to 4 are schematic views of the apparatus at three stages of operation.

Referring to FIG. I, the vaporizing device comprises a tubular member 1 having an inlet portion 2 with a reduced'bore 5, a central evaporationportion 3 with a bore 6 of increasing cross-sectional area from the inlet portion 2 to an outlet portion 4.'

Referring to FIGS. 1 to 4, the outlet portion 4 is connected to an analyzing device 10 and a vacuum source 11. The vacuum source is selectively isolated by valve means 12. I

The operation of the vaporizing device is as follows.

The liquid sample is drawn into'the tubular member by v the vacuum pumpthrough the restricted bore 5 into the tapered evaporation portion 3. The sample will rise through the section of increasing cross-sectional area 6 to a level 8 at which the sample is evaporated at a rate equal to the liquid inflow. Thereafter the liquid level will remain constant. 7

-At the surface where evaporation is taking place, in the case of water containing deuterium, a shallow isotopic gradient will be formed because of the ,difference in vapor pressures of water and deuterium. The first portion of the sample evaporated will be depicted in deuterium and hence the surface layer of liquid will be enriched in deuterium. Shortly thereafter isotopic equilibrium is set up in which the deuterium concentration of the vapor leaving the slightly enriched surface is equal to'the deuterium concentration of the liquid entering the sample tube. The equilibrium time for the apparatus used was less than 2 seconds. The vapor produced during this time is discarded.

The apparatus used for automated analysis is shown schematically in FIGS. 2 to 4. The tubular member 1 is connected to a vacuum source 11 and a mass spectrometer, chromatograph, or other analyzing device 10. The vacuum source 11 is selectively isolated from the mass spectrometer l0 and the tubular member 1 by a valve 12. The mass spectrometer 10 may be connected directly to the tubular member 1. The apparatusincludes means for moving the tubular member 1 up and down in accordance with the motion of a series of sample containers, e.g., l5 and 16 moved successively into position under the device 1. Means are also provided to shutoff and open the valve 12 in accordance with the motions of the sample containers and the tubular member 1, and required sample pressure in the analyzing device. v

The operation of the apparatus will now be described with reference to FIGS. 2 to 4.

. disrupted causing spurious results.

' discarded.

1 In FIG. 3 equilibriumohas beenfes tablished the valve l2 is close'd and the spectrometer is being-dosed with the sample. The analysis as required is then performed.

- In FIG. 4 the analysis has been completed, thetubular member 1 is raisedfrom the sample and the valvel2 isopened. The spectrometer and tubular member 1 are pumped out and vacuum dried. A new sample 16 is moved into position to replace sample 15, and the cycle repeated, orjthe cycle may be repeated using the same samplgas required. Alternatively the containers may remain stationary and the tubular member moved from one container to another.

a The manner in which the tubular member was made willnow be described. Almm bore glass capillary was pre-collapsed while heating with a flame. The bore was reduced until almost invisible, approximately 0.1mm, while maintaining the outside of the capillary at the same diameter. The capillary was then pulled to several feet to reduce the bore further and broken off at the point which has the desired bore.

Suitable dimensions for the tubular member were obtained by trial and error. The preferred inlet bore 5 diameter is to 30 microns. Below this range the inlet becomes increasingly susceptible to clogging.-

- The bore 5 may be increased above the preferred range if the capillary length is increased accordingly.

However, the increase in length increases the equilibrium time as it increases the time required for the sample a to be drawn up the additional length of tube.

The diameter of the meniscus 8 in the evaporation position 6 is preferably kept at 1mm or less. Above l'mm the upper evaporating layer of the A suitable pressure range at the outlet for the device described above is 0.01 torr to 7-torr.

sample is The precision obtainable 1 for a, deuterium. to

hydrogen concentration-ofl50 X l0" is; 0.lppm, which is equal to 'or better than that attained with manual operation of the same analysis.

1 Although the sample containerlS and l6 may be i made of any material, a'container of a material with which water formsaconvex meniscus is preferable. An

example of such a material is rxr'vlytetrat'louroethylene. Any foreign particles-which enterthe container will tend to move to the outside and reduce .the possibility of clogging the tubular memberinlet 5 when drawing the sample.

A method similar to that described may facilitate the. analysis of gas samples, in a pipe or the like. In this case the tubular member'does'no't vaporize the sample but otherwise maintains the same function of dosing the spectrometer.

it is to be understood limited to the analysis of water. The present method I may be usedtoprovide vaporized samples of a variety of liquids. Such other liquids would necessitate establishing suitable operating conditions, i.e. tubular member dimensions and vacuum level. v

at-isclaimedi .-An apparatus or vaporizing liquid-samples-comprising a tubular member having an inlet portion with a I reduced bore, a central evaporation portion having a bore of increasing cross-sectional area from the inlet portion to an outlet portion, said outlet portion con-: nected to first and secondpassage means, said first" passage means connected to a sample analyzing device and said second passage means connected to a vacuum source, and valve means releasably blocking said second passage.

2. The apparatus of claim 1 wherein said vacuum source provides a pressure between 0.01 torr and 7 tOlT.

v 3. The apparatus of claim 2 wherein the meniscus in the evaporation portion is kept below 1 mm in diame- 4. The apparatus of claim 3 for vaporizing water samples containing deuterium. I

v a a: a: a

that this invention is notto be I 

1. An apparatus for vaporizing liquid samples comprising a tubular member having an inlet portion with a reduced bore, a central evaporation portion having a bore of increasing crosssectional area from the inlet portion to an outlet portion, said outlet portion connected to first and second passage means, said first passage means connected to a sample analyzing device and said second passage means connected to a vacuum source, and valve means releasably blocking said second passage.
 2. The apparatus of claim 1 wherein said vacuum source provides a pressure between 0.01 torr and 7 torr.
 3. The apparatus of claim 2 wherein the meniscus in the evaporation portion is kept below 1 mm in diameter.
 4. The apparatus of claim 3 for vaporizing water samples containing deuterium. 